A scale model of the new San Francisco-Oakland Bay Bridge is seen at Autodesk's high-tech gallery in San Francisco, Calif. on Wednesday, Feb. 16, 2010. The design software developer is now opening its exhibits to the public once a week, each Wednesday afternoon.

Photo: Adam Lau, The Chronicle

A scale model of the new San Francisco-Oakland Bay Bridge is seen...

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A prototype of a character from the video game Spore, created by 3D-printing, is seen at Autodesk's high-tech gallery in San Francisco, Calif. on Wednesday, Feb. 16, 2010. The design software developer is now opening its exhibits to the public once a week, each Wednesday afternoon.

Photo: Adam Lau, The Chronicle

A prototype of a character from the video game Spore, created by...

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A live, interactive motion capture system, similar to what James Cameraon used to make his movie "Avatar" is seen in action at Autodesk's high-tech gallery in San Francisco, Calif. on Wednesday, Feb. 16, 2010. The design software developer is now opening its exhibits to the public once a week, each Wednesday afternoon.

Photo: Adam Lau, The Chronicle

A live, interactive motion capture system, similar to what James...

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Sheave room viewing area of the cable car barn seen from the Cable Car Museum in San Francisco, Ca., on Tuesday, February 9, 2010.

Photo: Liz Hafalia, The Chronicle

Sheave room viewing area of the cable car barn seen from the Cable...

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A model of Chrysler's Super Bee concept car is seen in comparison to a lifescale model of Ford's Mustang GT500 at Autodesk's high-tech gallery in San Francisco, Calif. on Wednesday, Feb. 16, 2010. The design software developer is now opening its exhibits to the public once a week, each Wednesday afternoon.

Photo: Adam Lau, The Chronicle

A model of Chrysler's Super Bee concept car is seen in comparison...

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Exhibits are seen at Autodesk's high-tech gallery in San Francisco, Calif. on Wednesday, Feb. 16, 2010. The design software developer is now opening its exhibits to the public once a week, every Wednesday afternoon.

Photo: Adam Lau, The Chronicle

Exhibits are seen at Autodesk's high-tech gallery in San Francisco,...

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The telescope called "Nellie" at Chabot Space & Science Center. Visitors can use the telescopes for free on Friday and Saturday nights.

Photo: Chabot Space And Science Center

The telescope called "Nellie" at Chabot Space & Science Center....

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A young visitor to the Palo Alto Junior Museum and Zoo watches as a Blue Indian Peafowl spreads its feathers on Friday, May 23, 2008, in Palo Alto, Calif.
Photo by Noah Berger / Special to the Chronicle

Photo: Noah Berger, Special To The Chronicle

A young visitor to the Palo Alto Junior Museum and Zoo watches as a...

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A man and woman take a morning stroll through the San Francisco Botanical Garden at Golden Gate Park in San Francisco, Calif., on Tuesday, March 24, 2009.

Autodesk doesn't have a visibility problem. As one of the world's biggest design software companies, the Bay Area business has influenced everything from the special effects in "Avatar" to the design of the new Cathedral of Christ the Light in Oakland.

But when Autodesk executives discovered that even some of their biggest clients didn't know the scope of what the company did, they dedicated 16,500 square feet in their San Francisco office at 1 Market St. to showcasing the work of its broad base of customers, with exhibits that display everything from skyscrapers to an airplane engine to surfboards that were designed with the software.

"What does Autodesk do?" Autodesk Senior Manager Jason Medal-Katz said during a recent tour. "Answering that question was a prime motivator for creating this space."

Last month, the gallery opened to the public on Wednesday afternoons, allowing free access to everything from a 9-foot-tall Lego dinosaur to a state-of-the-art software program that allows the user to build a small city in three dimensions. The coolness of the space - which includes a Shelby Mustang GT500 and a video that shows how it made its way into the second-floor showroom - put the Autodesk Gallery on the top of our list of the Best of Free in the Bay Area.

Accompanying this article are our five favorite free Bay Area institutions. Our only rule is that there had to be no set fee (though some places encourage donations) and there had to be a door or gate where someone could charge some money if they wanted to. Museums, galleries and arboretums qualified. Parks and beaches did not.

Please add your own choices to the SFGate.com version of this story.

Autodesk Gallery

Core demographic: Technology geeks, kids (especially older ones) and people who are excited about design.

Don't miss: The virtual cinematography exhibit, which allows visitors to grab a video camera and unleash their inner James Cameron - using MotionBuilder software to imitate some of the techniques he used while filming "Avatar"; the Lego hadrosaur (more specifically, a parasaurolophus), which has a box of Lego blocks so visitors can make their own additions; the models of the new Bay Bridge and Oakland's Cathedral of Christ the Light; the 3-D printer displays, which show several results of rapid prototyping; the view from the Embarcadero side of the gallery, which has several huge picture windows looking down on the Ferry Building Marketplace.

Hours of operation: Noon-5 p.m. Wednesday; guided tour at 12:30 p.m.

What's the catch? The Autodesk Gallery is a big tribute to Autodesk, which may disappoint the three people left on earth who don't expect large corporations to have their own interests in mind.

Cable Car Museum

Don't miss: The three 1870s-era cable cars; the Clay Street Railroad No. 8 grip car - the only remaining car from the first cable car company; the accounts of the 1906 earthquake and subsequent rebuilding of the cable car system; the cable car powerhouse (it's pretty much impossible to miss the huge engines and wheels pulling the cables, but make sure you stop downstairs to see the underground sheaves where the cables are routed to the street).

Hours of operation: 10 a.m. to 5 p.m. daily.

What's the catch? Parking is an absolute nightmare - best to pay for a cable car ride to the museum; the building is extremely loud (children and visitors with sensitive ears should bring earplugs); there's a Fisherman's Wharf-style touristy gift shop.

Chabot Space & Science Center weekend telescope viewings

Core demographic: Astronomy buffs, families and people looking for an innovative romantic date.

Don't miss: The center's nearly 130-year-old, 8-inch refractor telescope, which was housed in the original observatory in downtown Oakland; the 20-inch refractor telescope, built in 1914, which is the largest of its kind in the western United States open to the public; the Telescope Makers Workshop, where amateur astronomers can learn how to make cheap, surprisingly effective telescopes; the knowledgeable volunteers and Chabot scientists, who have a passion for both astronomy and the history of their telescopes.

Palo Alto Junior Museum and Zoo

Core demographic: Families and animal lovers interested in local species.

Don't miss: The 14 interactive museum exhibits, aimed toward younger school-age children, which teach basic physics and other scientific principles; the red-tailed hawk, raccoons, bats, sharks and other animals among the 50-plus species at the zoo, most of which are native to Northern California; Bobcat Ridge, the new home for the zoo's two bobcats, scheduled to open this summer; Rinconada Park, the 20-acre park adjacent to the zoo, which has a redwood grove, two playgrounds and a huge swimming pool with a children's wading area.

San Francisco Botanical Gardens

Core demographic: Gardening aficionados and people looking for a place to walk or read a book in peace and quiet.

Don't miss: Highlights in the 55-acre garden include the redwood trail, dwarf conifer garden, Japanese-influenced moon-viewing garden and McBean wildfowl pond and primitive plant garden; the children's programs, including docent-led tours for kids, children's garden and story time in the library at 10:30 a.m. on the first and third Sundays of the month; the annual plant sale, set for May 1, which is reasonably priced and offers a huge selection for gardeners.

What's the catch? The garden is more or less impressive depending on what's in bloom. The squirrels are notoriously aggressive. Donations are appreciated. (The Botanical Garden is facing severe cuts. If you can't afford to donate, go to the Web site and sign the petition.)